1. Field of the Invention
The invention relates to fluid level sensors and, more particularly, relates to a sensor for sensing the level of oil or another fluid in a receptacle based on changes of capacitance between parallel plates of a parallel plate capacitor. The sensor is particularly well-suited for use in machines that are subject to severe vibrations or otherwise are not amenable to float-type fluid level sensors.
2. Discussion of the Related Art
Fluid level sensors are widely used for sensing the level of fluids in receptacles in industrial and automotive applications. For instance, such sensors are typically used for monitoring the level of fuel in a fuel tank or the level of oil in an oil pan. These sensors typically comprise float-type sensors that include a buoyant float. The float simply rises and falls with the level of fluid in the receptacle and transmits an appropriate signal when the fluid level drops below a designated value.
Some applications, however, are ill-suited for float-type sensors. For instance, some machines are subject to severe vibrations or dramatic changes in orientation in use, resulting in significant agitation of the fluid within the monitored space as well as jostling of the float. These events result in reduced reliability or even complete inoperability of a float-type fluid level sensor. Examples of machines having these characteristics include rammers, breakers, and hammers.
Electronic fluid level sensors have been proposed and even implemented that lack the disadvantages of float-type sensors, but prior known electronic fluid level sensors have problems of their own. For instance, so-called tube-type capacitance fluid level sensors are known that are inserted downwardly into an upper opening in a crankcase such as an existing dipstick opening or a custom opening positioned much as a dipstick opening would be. The sensor includes inner and outer conductive tubes forming a capacitance bridge therebetween. Changes in fluid level within the receptacle are detected by changes in capacitance between the tubes, permitting the generation of a low fluid level warning signal or the like when the fluid level between the tubes drops below a designated value.
The need has therefore arisen for providing a simple, reliable, fluid level sensor.